1. Tell People
This makes you accountable. Tell everyone who will listen, says Joe Donovan, a Milwaukee runner who wrote the Essential Guide to Training for Your First Marathon.
"Only when you tell other people is it real," he says. It became a topic of conversation and support among his fiancée (now his wife) and co-workers, which helped him stick to his training.
The first person to tell is your doctor -- you want to make sure you’re OK to run long distances.
2. Set a Specific Goal
It's not as simple as saying your goal is to finish 13.1 miles (a half-marathon) or 26.2 (a full marathon), says Cathy Fieseler, MD, a veteran marathoner and ultra-distance runner.
Ask yourself why you’re running the race, she says. "Do you have a time goal? Are you trying to qualify for [the Boston marathon]? Are you doing it in memory of someone? Because you’re turning 40?"
Figuring that out, she says, will guide your training plan. For instance, if you're running in memory of someone, you may not care about how long it takes you. But if you want to finish within 4 hours, you might need a different program.
3. Make a Plan
You need a nuts-and-bolts training plan. You can get that online, or from a running coach, running club, or running publications.
If you're easily running 3 or 4 miles at a time now, plan to train for about 3 months before a half-marathon and about 5 months before a full marathon, says Todd Galati, an American Council on Exercise spokesman.
Your plan should be realistic. "I don't think you need to run every single day," Fieseler says. "Figure out what works for your life."
4. Don't Overdo It
Don't add miles too quickly, Galati says. The established rule is not to boost your miles by more than 10% per week.
Doing speed work can improve your times. For instance, run faster than usual for an interval of time, then drop back to your slower pace, and repeat. But don't increase mileage, do speed work, and tackle hills all at once, he says. That's too much.
Speed work can make you faster, ''but it also ups the risk of injury," Fieseler says, especially as you age. Be aware of the trade-off, she says.